Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-10-11
2002-08-27
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S057000, C347S010000
Reexamination Certificate
active
06439696
ABSTRACT:
This application is based on Japanese Patent Application No. 11-290270 (1999) filed Oct. 12, 1999, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing apparatus that prints on a print medium and more specifically to an ink jet printing apparatus capable of changing the amount of ink to be ejected.
2. Description of the Related Art
With the widespread use of office automation equipment such as personal computers and word processors in recent years, the use of printing apparatus, the peripheral devices of the equipment, is also spreading quickly. Among the printing systems of the printing apparatus there are a wire-dot system, a heat transfer system, and an ink jet system. These printing systems have their own print heads that perform a predetermined printing on a print sheet being fed.
There are growing demands on these printing apparatus for faster printing speed, higher resolution, higher image quality and lower noise. With the speeds of MPU's increasing and the integration levels of semiconductor memories becoming higher in recent years, the occasion of handling image data has increased. Hence, demands are increasingly growing for a high quality printing of images with half tone.
Among the methods for representing a halftone in the ink jet printing apparatus are a method which controls the number of dots applied to a unit area of a print medium (a pseudo halftone representation using binary values) and a method which uses a plurality of print heads with different ink ejection amounts or with different densities of ink and selects and activates an appropriate head according to a halftone to be printed.
However, there are the following problems with the conventional halftone representation methods.
With the pseudo halftone representation method using binary values, because a single pixel is represented with a plurality of dots, the resolution is degraded.
With the method of representing a halftone by using a plurality of heads with different ink ejection amounts or with different ink densities, the size reduction and space reduction are hindered, with additional problem of an increased cost. In a multivalued full color printing apparatus, in particular, it is necessary to use a plurality of heads for each color, making the realization of this halftone representation method very difficult.
Japanese Patent Application Laying-Open No. 55-132259 (1980) proposes a method which provides two electrothermal transducers (of the same or different sizes) in each nozzle to change a dot size and thereby realize a wide grayscale range and a high image quality with a very simple construction. This constitutes a very important technology in performing a multivalued printing. Provision of a plurality of electrothermal transducers in each nozzle, however, requires setting the nozzle size relatively large, giving rise to a problem that the resolution cannot be enhanced easily.
In the method that provides a plurality of electrothermal transducers in each nozzle and ejects different amounts of ink from each nozzle, the ejection speed is higher when the amount of ink ejected is large than when it is small. This causes variations in the ejection speed, which in turn causes deviations in the dot landing positions, resulting in a disturbed printed image.
It is also proposed that, to eject a small amount of ink a bubble produced by the activation of the electrothermal transducer is not brought into communication with an external air and that only when a large amount of ink is to be ejected, is the bubble brought into communication with an external air. For that purpose, a method has been proposed and implemented which gives one drive pulse for the ejection of one droplet when a small amount of ink is to be ejected and which gives a plurality of pulses for the ejection of one droplet when a large amount of ink is to be ejected. In this case, too, the above-described problem occurs, i.e., the ejection speed is higher when a large amount of ink is ejected than when a small amount is ejected, causing variations in the ink ejection speed and therefore deviations in the dot landing positions, which in turn disturbs an image.
In both of the above two methods, when the ink ejection amount is changed to form a large dot, followed by a small one, a large one, a large one, a small one, and so on for each pixel, meniscus vibrations occur, which in turn causes positional deviations of the meniscus in the nozzle portion. When the meniscus is tilted due to the positional deviation, the dot landing precision deteriorates significantly. Variations in the ink ejection amount should be kept to within ±10% but depending on driving conditions they are found to be as large as about ±20%. In the construction in which a plurality of electrothermal transducers are provided in each nozzle, if it is assumed that the nozzle that ejects a large ink droplet has twice the ink ejection amount of a nozzle that ejects a small ink droplet, the refill frequency of the large droplet ejecting nozzle is reduced to one-half that of the small droplet ejecting nozzle. The print speed of the ink jet printing apparatus therefore is limited by the refill frequency for the large droplet ejecting nozzle, making it impossible to obtain a sufficiently fast print speed.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-described conventional problems. It is therefore an object of the invention to provide an ink jet printing apparatus and an ink cartridge which can form a multivalued image by changing the ink ejection amount from each nozzle, easily enhance the resolution of the image, reduce ink ejection speed variations and meniscus vibrations when forming large or small dots, and produce high quality images, without using a plurality of electrothermal transducers in each nozzle or a plurality of print heads for ejecting ink droplets of the same color with different densities.
In the first aspect of the present invention, there is provided an ink jet printing apparatus comprising:
a print head having electrothermal transducers in ink ejection nozzles; and
drive control means for generating a drive pulse for controlling activation of the electrothermal transducers in accordance with print data;
wherein the drive pulse causes the electrothermal transducers to generate thermal energy to eject ink droplets from the nozzles onto a print medium to print an image;
wherein the drive control means changes a drive voltage and a drive pulse width simultaneously for the print head in accordance with the print data.
In the second aspect of the present invention, there is provided an ink jet printing apparatus comprising:
a print head having electrothermal transducers in ink ejection nozzles; and
drive control means for generating a drive pulse for controlling activation of the electrothermal transducers in accordance with print data;
wherein the drive pulse from the drive control means causes the electrothermal transducers to generate thermal energy to eject ink droplets from the nozzles onto a print medium to print an image;
wherein the drive control means, when ejecting small droplets, increases a drive voltage for the nozzles and shortens the drive pulse width for the nozzles and, when ejecting large droplets, reduces the drive voltage and relatively elongates the drive pulse width.
In the third aspect of the present invention, in an ink jet printing method of performing printing an image by utilizing a print head having electrothermal transducers in ink ejection nozzles, generating a drive pulse for controlling activation of the electrothermal transducers, supplying the drive pulse to the electrothermal transducers, and then causing the electrothermal transducers to generate thermal energy to eject ink droplets from the nozzles onto a print medium;
wherein a drive voltage and a drive pulse width for the print head are simultaneously changed in accordance with a print data.
In the fourth as
Murakami Shuichi
Tajika Hiroshi
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Stephens Juanita
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